Approach
Removal and replacement of the alley soils was impossible due to the presence of sensitive downtown electric and communication utilities, and with an adjacent 50-foot-deep basement wall across the alley, the only typically available alternative was expensive internal bracing. GeoEngineers challenged conventional thinking by:
- Designing a shoring system consisting of soldier piles with soil nails in the upper portion of the excavation and tiebacks below the adjacent building in the lower portion.
- Modeling the wall performance using a 2-D finite element model carefully calibrated to specific site conditions.
Seismic design of this tall building was also a challenge. GeoEngineers worked closely with the structural engineer to develop a series of site specific response spectra and acceleration records based on documented past experience for input into their 3-D dynamic model.
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